sperm whalePhyseter catodonalso called cachalotthe largest of the toothed whales, easily recognized by its enormous square head and narrow lower jaw. The sperm whale is dark blue-gray or brownish, with white patches on the belly. It is thickset and has small paddlelike flippers and a series of rounded humps on its back. Males attain a maximum length of about 19 metres (62 feet) and females about 12 metres.

Sperm whales are deep divers, commonly reaching a depth of about 350 metres, and have been found tangled in cables more than 1,000 metres below the surface. It is not uncommon for sperm whales to dive for an hour or more and then spend about 10 minutes at the surface breathing once every 10 seconds. They can cruise at a speed of 4 knots (7.4 km/hr; 4.6 mph) and swim in spurts at up to 20 knots.

These cetaceans are found in temperate and tropical waters throughout the world, usually in pods (groups) of about 15 to 20; solitary males, however, may wander into colder regions. Sperm whales attain sexual maturity at 7 to 13 years of age and physical maturity at 25 to 45 years and have been recorded to live as long as 62 years. They feed primarily on cephalopods, including the giant squid (Architeuthis dux). Weight figures are usually estimates, but in 1937 a pair of stranded male sperm whales were measured intact in The the Netherlands: one was 16 metres long and weighed 39 tons, and the other was 18 metres and 53 tons.

The sperm whale is the most evolutionarily modified of the toothed whales. The head constitutes one-third of the total body length and, it is estimated, greater than a third of the body weight. The lower jaw is usually equipped with 36 to 50 large conical teeth; the upper jaw holds a variable number of vestigial teeth that do not erupt. The head features an elaborately developed nose and upper lip where the fluid-filled spermaceti organ (which whalers called the case) is located; sperm oil and spermaceti were extracted from this fluid for lighting and lubrication. The spermaceti organ is unique to sperm whales. It has a volume as large as 2,000 litres (530 gallons) and can extend through 40 percent of the whale’s length.

The function of the spermaceti organ has not yet been conclusively demonstrated. Suggestions of its role pertain mostly to diving. It may close the nasal passages, act as a force pump for the bony nares, or serve in part as a hydrostatic organ by squeezing oil to one end or the other through contractions of its muscular sheath. Other theories suggest that it assists in the evacuation of the lungs prior to a deep dive, absorbs nitrogen at extreme underwater pressure, or acts as a buoyancy regulator to assist the whale while descending and ascending from deep dives. The spermaceti organ may serve these suggested purposes singly or in combination. It could even be a reverberation chamber used by the sperm whale in producing its unique pulsed signals, which are used for echolocation and communication.

Sperm whales were once commercially valuable and were hunted for several centuries. The White Whale hunted in Herman Melville’s novel Moby Dick (1851) is presumably an albino sperm whale. Ambergris, a material sometimes found floating in the sea, is thought to be formed in the sperm whale’s intestines around a core of undigested solid matter such as squid beaks.

Physeter is Greek for “blower,” an allusion to the sperm whale’s breathing. The pygmy and dwarf sperm whales (Kogia breviceps and K. simus) are the only other members of the family Physeteridae. These little-known dolphinlike whales are gray above and white below, and they are quite small—about 2.5 to 4 metres long. They are distributed worldwide in offshore waters from equatorial to temperate regions and have no commercial value. The family Physeteridae diverged from the rest of the toothed whales (suborder Odontoceti) very early. Large sperm whales with all of the characteristics of present-day sperm whales lived 20 million years ago during the Early Miocene Epoch (23.8 million to 16.4 million years ago). This early divergence makes conclusions about sperm whale relationships provisional.